1. Field of the Invention
The present invention relates to a process for preparing polyisobutene having a content of terminal vinylidene groups of at least 75 mol %.
2. Description of the Background
For the purposes of the present application, terminal vinylidene groups or terminal double bonds are those double bonds whose position in the polyisobutene macromolecule is described by the general formula
where R is a polyisobutenyl radical. The type and the proportion of the double bonds present in the polyisobutene can be determined with the aid of 1H or 13C NMR spectroscopy.
Such highly reactive polyisobutenes are used as intermediates for preparing additives for fuels and lubricants, as described, for example, in DE-A 27 02 604. The highest reactivity is exhibited by the terminal vinylidene groups having 2-methyl substitution, whereas neopentyl substitution or double bonds disposed further toward the center of the macromolecule, depending on their position in the macromolecule, exhibit only slight reactivity, if any, in the customary functionalization reactions. The proportion of terminal vinylidene groups in the molecule is therefore the most important quality criterion for this type of polyisobutene.
U.S. Pat. No. 5,286,823 describes a process for preparing highly reactive polyisobutenes by cationic polymerization of isobutene in the presence of boron trifluoride and secondary alcohols having from 3 to 20 carbon atoms and/or ethers having from 2 to 20 carbon atoms.
WO 93/10063 discloses boron trifluoride etherate complexes in which the ether has at least one tertiary carbon atom bonded to the ether oxygen atom. The complexes serve to polymerize olefins, in particular isobutene, to polymers having a high content of vinylidene groups.
EP-A 1 026 175 describes the preparation of isobutene polymers having at least 80 mol % of molecules with terminal vinylidene structure using complex catalysts of boron trifluoride, ether and alcohol and/or water in certain amounts.